1. Field of the Invention
One or more example embodiments relate to a method of performing beamforming in a terminal and the terminal for performing the method.
2. Description of Related Art
Beamforming may refer to determining of beam directions to transmit and receive beams at a highest signal level between a transmitter and a receiver to maximize utilization of a straightness and a path loss in a high frequency domain. To realize the beamforming, a device for acquiring information for the beamforming, and a device for determining a beamforming coefficient based on the acquired information may be used.
FIG. 1 illustrates an example of beamforming in a general mobile communication environment according to a related art.
As a frequency band increases, a straightness of a radio wave may increase, and a loss in a free space may also increase. Accordingly, to set an effective communication link in a terminal, beamforming may be necessarily performed.
The loss in the free space may have a relationship of Equation 1 as shown below, based on a Friis equation when an antenna gain is assumed to be “1.”
                    L        =                  20          ⁢                      log            10                    ⁢                                    4              ⁢              π              ⁢                                                          ⁢              Rf                        c                                              [                  Equation          ⁢                                          ⁢          1                ]            
In Equation 1, L denotes the loss, f denotes a frequency, and R denotes a distance between a transmission antenna and a reception antenna.
In an example, when a frequency is set to 2 gigahertz (GHz) at the distance R of “100” meters (m), a path loss of about 78.46 decibels (dB) may occur. In another example, when a frequency is set to 20 GHz based on the same distance, a path loss of about 98.46 dB may occur. Thus, it may be found that an additional loss of about 20 dB occurs as a frequency band increases.
Hereinafter, various beamforming methods according to the related art will be described.
FIG. 2 illustrates a method of acquiring beam information for beamforming using a feedback channel and a communication channel between a transmitter (TX) and a receiver (RX) according to the related art.
In the method of FIG. 2, the communication channel and the feedback channel may be used to acquire beam information for beamforming.
For example, a receiver may receive a signal from a transmitter through the communication channel, may extract information of beams and may determine a reception beamforming. Also, the receiver may transmit information of received beams to the transmitter through the feedback channel, and accordingly a transmission beamforming of the transmitter may be determined. In this example, various beamforming methods according to the related art may be used based on whether the communication channel and the feedback channel are present.
In a beamforming method, when a feedback channel is absent, a direction of a received beam may be determined based on an intensity of a signal received through a communication channel, and a direction of a transmitted beam in a transmitter may be determined as all directions. In another beamforming method, information for beamforming may be transmitted between a transmitter and a receiver based on a type of feedback channels (for example, based on a transmission of information of 1 bit indicating yes or no, or a portion or all of beamforming information).
FIG. 3 illustrates an example of beamforming using an array antenna according to the related art.
A beamforming coefficient may be determined to acquire beam information for beamforming, which may indicate a method of determining coefficients, for example, coefficients c1, c2 and cN, multiplied for each antenna element of the array antenna as shown in FIG. 3. Based on values of the coefficients, a width and a direction of a synthesized beam of the array antenna may be determined.
The determining of the beamforming coefficient is limited to the coefficients of the array antenna as described above, however, may need to be interpreted as comprehensive meaning of determining a direction of a high directional antenna. For example, in a horn antenna, determining of a beamforming coefficient may indicate determining of a boresight that is a direction of the horn antenna.
As described above, due to a considerable path loss in a high frequency domain, for example, a millimetric wave, it is impossible to avoid use of a high directional antenna.
Accordingly, when the high directional antenna is used, the following issues may occur.
A link setup time required to search for all directions may increase because it is impossible to know a direction of a beam during an initial communication link setup.
Also, a communication link is highly likely to be broken due to a sudden change in a transmitter and a receiver or surroundings of the communication link when a high directional antenna is used for a frequency with a strong straightness. In many cases, for example, a case in which a direction of a face is changed by suddenly turning a head while talking over a terminal in contact with the face, the communication link may be broken.
FIGS. 4A and 4B illustrate a blocking phenomenon in a line of sight (LOS) communication link situation according to the related art.
For example, when a communication link is set between a TX and an RX as shown in FIG. 4A, a specific obstacle may cover the communication link.
In this example, received power in the TX and the RX may change as shown in FIG. 4B. A low received power may correspond to a point in time at which an obstacle appears between the transmitter TX and the receiver RX.
The above phenomenon in which receiving power of the communication link changes due to the obstacle may be referred to as a “blocking phenomenon.” The blocking phenomenon may also occur in a high directional antenna.